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Thread: Broken parts

  1. #1
    guyintense's Avatar
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    Default Broken parts

    I don't break parts too often, a couple of bottom brackets a few cracked frames an exploded Nuke proof hub but this part looks as though it was doomed from the start. Pretty amazing it lasted as long as it did, 6 years.
    001.JPG

  2. #2
    donevwil is offline VSalonistas
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    Default Re: Broken parts

    No flesh in the photo so I guess you survived unscathed. What brand/type crank is that ?

    I tend to run components until they die, but have never broken a crank.. yet.

  3. #3
    Too Tall's Avatar
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    Default Re: Broken parts

    Go play the lottery ASAP. You are one lucky MoFo.

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    guyintense's Avatar
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    Default Re: Broken parts

    Quote Originally Posted by Too Tall View Post
    Go play the lottery ASAP. You are one lucky MoFo.
    Funny, I didn't feel that way when I was laying there in the dirt but looking back on all the trails a rode with that crank including Porcupine rim and Poison Spider portal and to have it snap on a relatively flat trail half a mile from the car, I guess I am one lucky Mo Fo.

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    ohsnapitberic is offline VSalonistas
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    Default Re: Broken parts

    that's pretty intense. I break parts, but not that badly!

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    Mabouya is offline VSalonistas
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    Default Re: Broken parts

    Looks like that crack was growing for quite a while before it reached critical size. What's most interesting IMO is that it seems to have been caused / propagated by lateral loading, not vertical loads or torsion. You would think that at that location the most important stress would be from the vertical shear and the torsion. (Kind of close to the load application point for it to be bending.)

    Caveat: it's tough to tell from this view what the angle of failure surface is relative to the crank arm. Torsion is greatest at a 45* angle (for a circular cross-section) and shear is uniform across the cross-section normal to the axis of the "beam."

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    david's Avatar
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    Default Re: Broken parts

    whoa. that thing looks like it was made out of tin foil.
    ctfd

  8. #8
    monadnocky's Avatar
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    Default Re: Broken parts

    Someone ask Echelon_John about his (snapped) circa 1987 Modolo stem and its intimate relationship with his right femoral artery.
    ... or it may have been a 3TTT, I don't recall (and I wasn't there).

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    dlflemingos is offline VSalonistas
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    Default Re: Broken parts

    Quote Originally Posted by Mabouya View Post
    Looks like that crack was growing for quite a while before it reached critical size. What's most interesting IMO is that it seems to have been caused / propagated by lateral loading, not vertical loads or torsion. You would think that at that location the most important stress would be from the vertical shear and the torsion. (Kind of close to the load application point for it to be bending.)

    Caveat: it's tough to tell from this view what the angle of failure surface is relative to the crank arm. Torsion is greatest at a 45* angle (for a circular cross-section) and shear is uniform across the cross-section normal to the axis of the "beam."
    Agree. Looks like it's from a side load. Looks like it originated right in the middle of the side and from the striations is a bending load all due to a repeated side load.
    I also can't figure out how the pieces go back together perhaps due to an optical illusion. Seems like one failure plane should slope the other way. Would be nice to have some more/better pictures or angles or maybe a diagram. You happen to have a SEM (Scanning Electron Microscope)?
    You said 6 years but how many miles on this crank?

  10. #10
    andrew flowers is online now VSalonistas
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    Default Re: Broken parts

    I have a great scar on my left ankle from a crank failure, just above the tendon.

    Had a mtb crank shear just like that while out stunting around one night

    went straight into my leg

    22 internal stitches later I have a two dollar coin (for the canadians) sized scar there for life.

    my mom was not thrilled to get the call at midnight on a schoolnight to bring me to the hospital, but that is part of being young and dumb.

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    steve garro's Avatar
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    Default Re: Broken parts

    I've done a few of those.
    Worst was dropping off a 3' ledge to flatbottom, sheared the crank and went to the bars so hard (didn't wreck) but dislocated my right shoulder. Still is jacked.
    I used to shear pedal spindles, always the right one, and always uphill.
    Old hollow BB spindles too.
    - Garro.
    Steve Garro, Coconino Cycles.
    Frames & Bicycles built to measure and Custom wheels
    Hecho en Flagstaff, Arizona desde 2003
    www.coconinocycles.com
    www.coconinocycles.blogspot.com

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    al415's Avatar
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    Default Re: Broken parts

    When I started riding and road racing in the mid 1980's, I went through a period of snapping chains. Always on climbs, always out of the saddle. I still have SOME real teeth left. I've been pretty lucky since then. The odd mangled derailleur. A snapped alloy frame or two (GT's seemed to be made of tinfoil in the 90's). That picture up top makes me shiver.

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    David Tollefson's Avatar
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    Default Re: Broken parts

    I've been very fortunate in my biking years that most broken parts never caused me to touch ground. I've broken rear derailleurs (several), spokes, a shift lever, and a few MTB frames (always found the crack before catastrophic failure). The latest was this little number that I got off eBay for $3.25 plus $30 shipping.
    MTB Full resize.jpg
    This pic doesn't really do it justice -- that crack extends under the tube at the weld all the way to the other side, and up the other side of the tub an equal amount.
    Crack 1 resize.jpg
    And this one on the seat tube, about 1/2 way around as well. Yup, the entire drive train was about to drop of the bike...
    Crack 2 resize.jpg
    I suppose I shouldn't complain, as this bike lasted me a good 4 years of pretty much maintenance-free riding while I left it at work, outdoors, through all kinds of weather (under cover, at least).

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    steve garro's Avatar
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    Default Re: Broken parts

    Quote Originally Posted by David Tollefson View Post
    I've been very fortunate in my biking years that most broken parts never caused me to touch ground. I've broken rear derailleurs (several), spokes, a shift lever, and a few MTB frames (always found the crack before catastrophic failure). The latest was this little number that I got off eBay for $3.25 plus $30 shipping.
    MTB Full resize.jpg
    This pic doesn't really do it justice -- that crack extends under the tube at the weld all the way to the other side, and up the other side of the tub an equal amount.
    Crack 1 resize.jpg
    And this one on the seat tube, about 1/2 way around as well. Yup, the entire drive train was about to drop of the bike...
    Crack 2 resize.jpg
    I suppose I shouldn't complain, as this bike lasted me a good 4 years of pretty much maintenance-free riding while I left it at work, outdoors, through all kinds of weather (under cover, at least).
    Man, just about every raised chainstay bike broke.
    Haros, Mantis, Yeti, Nishiki........
    - Garro.
    Steve Garro, Coconino Cycles.
    Frames & Bicycles built to measure and Custom wheels
    Hecho en Flagstaff, Arizona desde 2003
    www.coconinocycles.com
    www.coconinocycles.blogspot.com

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    EricKeller's Avatar
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    Default Re: Broken parts

    probably started from a surface ding in the center of the crank arm. It had to be visible for quite some time as a large crack (months, a year?), although you would have to look close because it would be closed if not being ridden. Pretty common if the internet is to be believed, google image search shows a large number of similar failures

    That's why my motto is "clean your bike."

  16. #16
    Michael Roy's Avatar
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    Default Re: Broken parts

    I've broken 3 cranks and one fork over the years - all while riding ("JRA"), and all without incident or injury. Riding to work one day on the cross bike my front brake was rubbing. I adjusted it. Riding home that night I had to adjust it again. I couldn't figure out what was wrong, so I lifted the front of the bike to spin the front wheel to check it, only to have the lower part of one side of the fork fall off! It had rusted through and the upper part was resting on the lower part only due to the weight pressing on it and the jagged break. I was pretty amazed and fortunate.

  17. #17
    PDAR is offline VSalonistas
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    Default Re: Broken parts

    I sheared off a World Class bottom bracket drive side spindle after about 9000 miles. Happened while climbing at about 8 mph so it wasn't a big deal.

  18. #18
    guyintense's Avatar
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    Default Re: Broken parts

    I had probably 6000 miles on this crank. I rode one just like it on my Uzzi Sl for over 9 years without incident. Here's a few more photos.
    Attached Images Attached Images

  19. #19
    bigbill's Avatar
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    Default Re: Broken parts

    I broke a DA 7400 crank arm at the pedal hole. I had a tendency to smack pedals in crit corners so I don't blame shimano. I broke several short cage XT derailleurs and I do blame that on shimano. I ended up racing a whole season with a light action with bullseye pulleys with no failures.

  20. #20
    thollandpe's Avatar
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    Default Re: Broken parts

    Is it my eyes or do you have a 2nd crack parallel to the big one and about halfway between there and the pedal eye?

    Maybe even a 3rd on the other side, about the same distance away?

    If either is the case, go play the lottery again. And go to church next week. TH

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